An acrylic rubber has good heat resistance, oil resistance and other properties, and therefore, is widely used as a material for rubber parts to be fitted in contact with metal or oil, such as seals, hoses, vibration insulators, tubes and belts in an automobile industry and related industries. For the acrylic rubber used for these rubber parts, a reduced permanent set, a reduced corrosive action for metal and a more enhanced oil resistance, as well as good heat resistance and good cold resistance, are required.
When an uncrosslinked acrylic rubber is kneaded by a Banbury mixer or a roll mill, the acrylic rubber tends to easily stick to the inner metal wall of the Banbury mixer or the surface of the roll. This leads to a decrease of recovery ratio, and further, cleaning of the Banbury mixer or the roll mill is required. It is, therefore, eagerly desired to reduce the stickiness of the acrylic rubber to a metal surface.
Further, when an acrylic rubber is processed, scorch is liable to occur, namely, a crosslinking reaction easily proceeds. Thus, prevention or minimization of scorch also is desired.
A crosslinked rubber product of a crosslinkable rubber composition comprising an acrylic rubber having copolymerized therein a mono-lower-alkyl ester of fumaric acid, an aromatic diamine crosslinking agent, and a guanidine compound crosslinking accelerator has been proposed as a crosslinked rubber product exhibiting a reduced corrosive action for metal and having good oil resistance in Japanese Unexamined Patent Publication No. H11-92614. This crosslinked rubber product further has good heat-aging resistance and cold resistance, but exhibits poor resistance to deteriorated oil and scorch stability, and tends to stick to a metal surface.
An acrylic rubber composition comprising a copolymer made from an alkoxy acrylate, 10–15% by weight of acrylonitrile and a required amount of a crosslinking monomer has been proposed in Japanese Unexamined Patent Publication No. 2001-146540, which can exhibit an enhanced impermeability to fuel, while good sour gasoline resistance and good amine resistance are kept when the rubber composition is used for a fuel hose for automobiles. However, this rubber composition has a problem such that the cold resistance and heat resistance are reduced.
To reduce the stickiness of an acrylic rubber to a metal surface, it is adopted to incorporate an internal release agent such as ester wax, paraffin wax, an organic acid metal salt and silicone oil in an acrylic rubber. However, when the acrylic rubber having incorporated therein an internal release agent is crosslinked, permanent set and other properties of a resulting crosslinked product are deteriorated.